[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / block / request.txt


struct request documentation

Jens Axboe <jens.axboe@oracle.com> 27/05/02

1.0
Index

2.0 Struct request members classification

	2.1 struct request members explanation

3.0


2.0
Short explanation of request members

Classification flags:

	D	driver member
	B	block layer member
	I	I/O scheduler member

Unless an entry contains a D classification, a device driver must not access
this member. Some members may contain D classifications, but should only be
access through certain macros or functions (eg ->flags).

<linux/blkdev.h>

2.1
Member				Flag	Comment
------				----	-------

struct list_head queuelist	BI	Organization on various internal
					queues

void *elevator_private		I	I/O scheduler private data

unsigned char cmd[16]		D	Driver can use this for setting up
					a cdb before execution, see
					blk_queue_prep_rq

unsigned long flags		DBI	Contains info about data direction,
					request type, etc.

int rq_status			D	Request status bits

kdev_t rq_dev			DBI	Target device

int errors			DB	Error counts

sector_t sector			DBI	Target location

unsigned long hard_nr_sectors	B	Used to keep sector sane

unsigned long nr_sectors	DBI	Total number of sectors in request

unsigned long hard_nr_sectors	B	Used to keep nr_sectors sane

unsigned short nr_phys_segments	DB	Number of physical scatter gather
					segments in a request

unsigned short nr_hw_segments	DB	Number of hardware scatter gather
					segments in a request

unsigned int current_nr_sectors	DB	Number of sectors in first segment
					of request

unsigned int hard_cur_sectors	B	Used to keep current_nr_sectors sane

int tag				DB	TCQ tag, if assigned

void *special			D	Free to be used by driver

char *buffer			D	Map of first segment, also see
					section on bouncing SECTION

struct completion *waiting	D	Can be used by driver to get signalled
					on request completion

struct bio *bio			DBI	First bio in request

struct bio *biotail		DBI	Last bio in request

struct request_queue *q		DB	Request queue this request belongs to

struct request_list *rl		B	Request list this request came from
Commit	Line	Data
1da177e4 LT	1
	2	struct request documentation
	3
26bbb29a	4	Jens Axboe <jens.axboe@oracle.com> 27/05/02
1da177e4 LT	5
	6	1.0
	7	Index
	8
	9	2.0 Struct request members classification
	10
	11	2.1 struct request members explanation
	12
	13	3.0
	14
	15
	16	2.0
	17	Short explanation of request members
	18
	19	Classification flags:
	20
	21	D driver member
	22	B block layer member
	23	I I/O scheduler member
	24
	25	Unless an entry contains a D classification, a device driver must not access
	26	this member. Some members may contain D classifications, but should only be
	27	access through certain macros or functions (eg ->flags).
	28
	29	<linux/blkdev.h>
	30
	31	2.1
	32	Member Flag Comment
	33	------ ---- -------
	34
	35	struct list_head queuelist BI Organization on various internal
	36	queues
	37
	38	void *elevator_private I I/O scheduler private data
	39
	40	unsigned char cmd[16] D Driver can use this for setting up
	41	a cdb before execution, see
	42	blk_queue_prep_rq
	43
	44	unsigned long flags DBI Contains info about data direction,
	45	request type, etc.
	46
	47	int rq_status D Request status bits
	48
	49	kdev_t rq_dev DBI Target device
	50
	51	int errors DB Error counts
	52
	53	sector_t sector DBI Target location
	54
	55	unsigned long hard_nr_sectors B Used to keep sector sane
	56
	57	unsigned long nr_sectors DBI Total number of sectors in request
	58
	59	unsigned long hard_nr_sectors B Used to keep nr_sectors sane
	60
	61	unsigned short nr_phys_segments DB Number of physical scatter gather
	62	segments in a request
	63
	64	unsigned short nr_hw_segments DB Number of hardware scatter gather
	65	segments in a request
	66
	67	unsigned int current_nr_sectors DB Number of sectors in first segment
	68	of request
69
70	unsigned int hard_cur_sectors B Used to keep current_nr_sectors sane
71
72	int tag DB TCQ tag, if assigned
73
74	void *special D Free to be used by driver
75
76	char *buffer D Map of first segment, also see
77	section on bouncing SECTION
78
79	struct completion *waiting D Can be used by driver to get signalled
80	on request completion
81
82	struct bio *bio DBI First bio in request
83
84	struct bio *biotail DBI Last bio in request
85
165125e1	86	struct request_queue *q DB Request queue this request belongs to
1da177e4 LT	87
1da177e4 LT	88	struct request_list *rl B Request list this request came from